Fixed-node quantum Monte Carlo for molecules

Journal Article · Wed Dec 01 04:00:00 EST 1982 · J. Chem. Phys.; (United States)

OSTI ID:6705530

Reynolds, P J; Ceperley, D M; Alder, B J; Lester, Jr, W A

The ground-state energies of H/sub 2/, LiH, Li/sub 2/, and H/sub 2/O are calculated by a fixed-node quantum Monte Carlo method, which is presented in detail. For each molecule, relatively simple trial wave functions Psi/sub T/ are chosen. Each Psi/sub T/ consists of a single Slater determinant of molecular orbitals multiplied by a product of pair-correlation (Jastrow) functions. These wave functions are used as importance functions in a stochastic approach that solves the Schroedinger equation by treating it as a diffusion equation. In this approach, Psi/sub T/ serves as a ''guiding function'' for a random walk of the electrons through configuration space. In the fixed-node approximation used here, the diffusion process is confined to connected regions of space, bounded by the nodes (zeros) of Psi/sub T/. This approximation simplifies the treatment of Fermi statistics, since within each region an electronic probability amplitude is obtained which does not change sign. Within these approximate boundaries, however, the Fermi problem is solved exactly. The energy obtained by this procedure is shown to be an upper bound to the true energy. For the molecular systems treated, at least as much of the correlation energy is accounted for with the relatively simple Psi/sub T/'s used here as by the best configuration interaction calculations presently available.

• Research Organization: National Resource for Computation in Chemistry, Lawrence Berkeley Laboratory, University of California, Berkeley, California 94720
• OSTI ID: 6705530
• Journal Information: J. Chem. Phys.; (United States), Journal Name: J. Chem. Phys.; (United States) Vol. 77:11; ISSN JCPSA
• Country of Publication: United States
• Language: English

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74 ATOMIC AND MOLECULAR PHYSICS
ALKALI METAL COMPOUNDS
ALKALI METALS
ELECTRONIC STRUCTURE
ELEMENTS
ENERGY
ENERGY LEVELS
FUNCTIONS
GROUND STATES
HYDRIDES
HYDROGEN
HYDROGEN COMPOUNDS
LITHIUM
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LITHIUM HYDRIDES
MECHANICS
METALS
MOLECULES
MONTE CARLO METHOD
NONMETALS
OXYGEN COMPOUNDS
QUANTUM MECHANICS
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WAVE FUNCTIONS